Integrated pump-control system using a unitized pump

ABSTRACT

An integrated fuel pump and control system has a unitized pump which includes three pumping circuits. A first pump circuit includes a positive displacement gear pump to provide fuel to a gas turbine engine from startup to just below idle. A second pump circuit includes a high-flow centrifugal pump, and a third circuit includes a low-flow centrifugal pump. A pump switching arrangement automatically switches from the first circuit at an engine speed slightly below that of ground idle to either the second or third circuit depending on the engine fuel requirements.

United States Patent [72] Inventor Robert S. Lanctot 2,780,172 2/1957Coar 417/286 Long Meadow, MESS. 2,812,715 11/1957 Redding et 417/248[21] Appl. No. 17,748 2,941 ,473 6/1960 Lorenz 417/248 [22] Filed Mar.9,1970 2,968,348 1/1961 Fortmann. 417/286 [45] Patented Oct. 19, 19713,026,929 3/1962 Bums t 417/286 [73] Assignee Chandler Evans Inc.3,279,522 /1966 Norris et a1. 417/79 west Hartford Conn PrimaryExaminer-William L. F reeh Attorney-Radford W. Luther [54] INTEGRATEDPUMP-CONTROL SYSTEM USING A UNIT [ZED PUMP 26 Claims, 5 Drawing Figs.

[52] US. Cl 417/253,

417/76, 4 7/ 8, 417/427 ABSTRACT: An integrated fuel pump and controlsystem has [5 lnt. a unitized pump which includes three i it A fi tF0413 49/00, F041) 41/06 pump circuit includes a positive displacementgear pump to of Search 79, provide fuel to a gas turbine engine fr stanp t j t b l 426, 427 idle. A second pump circuit includes a high-flowcentrifugal pump, and a third circuit includes a low-flow centrifugalReferences Cited pump. A pump switching arrangement automaticallyswitches UNITED TATE PAT from the first circuit at an engine speedslightly below that of 2,506,611 5/1950 Npal et a1. 417/216 ground idleto either the second or third circuit depending on 2,549,897 4/1951Everell 417/287 the engine fuel requirements.

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sum w FIG 4 PUMP PXEJSZ/FE INTEGRATED PUMP-CONTROL SYSTEM USING A UNITIZED PUMP BACKGROUND OF THE INVENTION The invention relates generallyto fluid pumping systems. More particularly, this invention pertains tofuel control systems for gas turbine engines.

Fuel controls for gas turbine engines commonly include positivedisplacement pumps to meet engine startup and lowspeed requirements.Positive displacement pumps are employed to meet these requirementsbecause of their inherent dry lift and high-output pressurecapabilities. However, the use of positive displacement pumps throughoutthe entire range of engine operation presents certain problems,prominent among which are the fuel heating caused by high bypass flowsand the ability of the pump to handle contaminated fuel. The unitizedfuel pump, shown and described in U.S. Pat. application No. 767,293,filed Oct. 14, 1968, and now U.S. Pat. No. 3,547,557, provides solutionsto the problems of fuel heating and contaminated fuel pumping. In orderto incorporate the aforementioned pump into a jet engine fuel system,particularly of the afterbuming type, it may be necessary that thepump-fuel control combination be capable of providing pump switchinglogic to maintain adequate transient fuel-metering accuracy.

SUMMARY OF THE INVENTION The invention provides an integratedpump-control system which possesses the necessary responsecharacteristics to maintain adequate transient fuel-metering accuracy.The invention achieves minimization of the transient disturbance whichoccurs when the system is switched from one pump to another.

Briefly stated, an integrated pump-fuel control includes a unitized pumphaving a positive displacement pump and two centrifugal pumps. Thepositive displacement pump is used for starting and suppliesacceleration fuel flow up to an engine speed slightly below that ofground idle. Thereafter, transition to operation on one of thecentrifugal pumps occurs automatically. One of these centrifugal pumpsis a high-flow unit, and the other is a low-flow unit. At alloperational engine speeds from ground idle to maximum, one of thesecentrifugal pumps provides fuel to the engine. The fuel metering systemsfor the gas generator and the augmentor operate in parallel off the pumpdischarge. The pump-control system includes a switching logicarrangement which senses the engine speed, the pressure differentialacross the control, and the total fuel flow demanded of the control. Theflow-metering arrangement is used during all three modes of pumpoperation. This arrangement precludes discontinuous "switching from onemode of pressure regulation -to another. THis discontinuous switchingwould otherwise be detrimental to the performance of the fuel controlsince it would engender large transient fuelmetering errors. Switchingfrom operation on the positive displacement pump to operation on eitherof the centrifugal pumps is accomplished in such a manner that thefuel-metering systems operate in a continuous fashion.

Accordingly, a primary object of the invention is to provide anintegrated pump-control system for gas turbine engines.

Another object is to provide an integrated pump-control systemincorporating a unitized pump wherein switching logic is provided forthe unitized pump.

Still another object is to provide an integrated pump-control systemhaving a unitized pump wherein means are provided to prevent largetransient fuel-metering errors.

A further object is to provide an integrated pump-control system for agas turbine engine incorporating an afterburner.

A still further object is the provision of an improved unitized pump.

Other objects and advantages of the present invention will be apparentand understood from the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are respectiveportions of a block diagram of an integrated pump-control systemembodying the present invention.

FIG. 2 is a schematic view of the unitized fuel pump of FIG. 1A.

FIG. 3 is a schematic view of a gas turbine engine having anafterburner.

FIG. 4 is a graph illustrating the performance of the integratedpump-control system of FIGS. IA and 1B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT description of preferredembodiment The integrated pump-control system of FIGS. IA and 1B isadapted to supply fuel to either a conventional or afterburning-type jetengine such as that shown in FIG. 3. The engine of FIG. 3 comprises acompressor rotor 10 and a turbine rotor 12 which are mounted to rotateunitarily within an engine casing 14. Compressed air from the rotor I l)passes through combustor 16. The hot gas stream from the combustor I6drives the rotor 12 and hence compressor 10. An afterbumer 13 is mountedaft of rotor 12 to add additional fuel to the hot gases emergingtherefrom for providing additional thrust. The com pressor, rotor andcombustor are commonly designated by the term gas generator, and theafterburner 118 is also known as an augmentor.

Referring now to FIG. 2, wherein the unitized pump of FIG. 1A isschematically illustrated, fuel enters an inlet which includes a conduit20. Assuming that the speed (N,,,) of the gas generator is below that ofground idle, fuel flows from inlet conduit 20 through a conduit 22 tothe outlet of a jet pump, generally designated at 24. The jet pump 24includes a housing 26 having a nozzle 28 mounted at one end thereofwithin a chamber 30. Nozzle 28 discharges into a venturi section 32which is joined transversely by an induced flow inlet 34. When the speedof the gas generator is between zero and slightly below that of groundidle (e.g. 55 percent), flow proceeds from conduit 22 into the outlet ofthe jet pump. Fuel flows away from the jet pump in a conduit 36 and isdelivered thence into a conduit 38 via a gear pump unloading valve 40,the details of which are described hereinafter. Fuel flowing in conduit38 away from the gear pump unloading valve is delivered via conduit 38to the inlet of a positive displacement gear pump, generally indicatedat 42.

Positive displacement gear pump 42 is of the sealing block or wear blocktype. This type of pump is well known in the art and is shown, forexample, in U.S. Pat. Nos. 2,705,259 and 3,208,393. Only the basicelements of the sealing block pump 42 are represented in the schematicdiagram of FIG. 2, and it will, of course, be understood that the pumpis in a suitable housing 43 and incorporates all of the structurenecessary to constitute a sealing block pump as disclosed in theaforementioned patents. Pump 42 includes meshing gears 44 and 46 and awear or sealing block 48 adapt-ed to engage the gears peripheries, thegears being depicted somewhat in perspective to show the cooperationbetween the gears and the sealing block 48. The gears 44 and 46 aredisposed within their housing 43 in a suitable cavity'or recess 50. Thediameter of gear 46 is greater than that of gear 44 for reasonsexplained hereinafter.

The adjacent arcuate wear surfaces of sealing block 48 are contoured tosimultaneously contact the peripheries (tooth tips) of gears 44 and-46.If desired, side plates may be provided for the positive displacementpump to create a region of high fluid pressure in the area of meshingcontact between gears 44 and 46. The construction of such side plates iswell known to those skilled in the art, and is exemplified in U.S. Pat.No. 3,427,985.

Gears 44 and 46 are mounted on suitable journals (not shown) forrotation, and gear 44 is connected to a shaft 52 which is adapted to bedriven by the engine of FIG. 3 by means of a suitable connection to thegear box thereof. Input shaft 52 rotates in the direction indicated bythe arrow to drive gear pump 42.

A piston and shaft assembly 54 is mounted for axial sliding movementwithin a cylinder 56. The left end of the piston and shaft assembly isdirectly connected tosealing block 48 to urge the same into engagingcontact with gears 44 and 46. An axial passage 58 extends completelythrough the piston and shaft assembly 54 to communicate dischargepressure to the right face of the piston 54 in order to urge the sealingblock into firm engagement with the teeth of gears 44 and 46. Sealingblock 48 is also urged into peripheral sealing engagement with the teethof the gears 44 and 46 by a spring 60, disposed within the right end ofcylinder 56. Thus, as the pump is started, sealing block 48 is urgedinto sealing engagement with the gears thereof solely by means of thespring 60. As the discharge pressure from the positive displacement pumpincreases, due to the increasing speed of rotation of gears, thedischarge pressure ported behind the piston 54 supplements the forceexerted by the spring 60 to generate a greater force upon sealing block48. The outlet of positive displacement pump 42 discharges fuel to afirst discharge conduit 62. The outlet of first discharge conduit 62communicates with a chamber 64 in which is positioned a spring-loadedcheck valve 66 which pennits pressurized fuel to be discharged from theoutlet of conduit 62. After a predetermined discharge pressure isattained, the pressurized fuel in chamber 64 is delivered to a mainoutlet conduit 68 via passage 70, chamber 72 and conduit 74. The rightend of conduit 74 is in communication with still another chamber 76.Chambers 72 and 76 function to receive fuel flow from the respectivecentrifugal pumps as is explained hereinafter. Thus, chambers 64, 72 and76, passage 70 and conduit 74 form a discharge manifold for the unitizedpump which discharges fluid at a pressure P The pressurized fuel in themain outlet conduit 68 is delivered to the fuel control for eventualmetered delivery to the engine.

The above-described fluid flow circuit defined by conduit 22, jet pump24, conduit 36, gear pump unloading valve 40, conduit 38, conduit 62 andthe fuel discharge manifold constitute the first flow circuit whichdelivers fuel to the engine fuel control at startup and during low-speedoperation. The first pumping circuit is then characterized by the drylift and highpressure capabilities of positive displacement pump 42.

inlet conduit is also connected to an inlet fuel shutoff valve generallydesignated at 78. inlet fuel shutoff valve 78 includes a generallycylindrical cavity 80, in communication with an inlet port 82 and anoutlet port 84, the inlet port 82 being fluidly connected to inletconduit 20. At each end of the cavity 80 are pressure-sensing ports 86and 88 which respectively communicate with boost pressure P that is, thepump inlet pressure, and a signal pressure which is dictated by thespeed of the gas generator. Speed signal conduit 90, which embodies anorifice 93, is adapted to direct a preidle speed signal to the inletfuel shutoff valve 78. A spool 92, having lands 94 and 96, is slideablydisposed within cavity 80 for sliding movement therein. The lands 94 and96 are shaped as cups to reduce the overall system weight. A compressionspring 98, mounted in the left portion of the cavity 80, contacts land94 to urge the spool towards the right to a position in which land 94covers inlet port 82, this position being illustrated in FIG. 2. Thesignal pressure from signal conduit 90 is transmitted to land 96 viaport 88. Thus, the opposing axial forces acting on the Spool 92 arederived from the boost pressure acting in concert with the spring 98 andthe signal pressure acting upon land 96.

Referring again briefly to FIG. 3, an actual speed signal generator 100is mechanically or electrically connected to the gas generator andgenerates an output signal E reflecting the speed of the gas generatorN, (and hence the speed of the centrifugal pumps). it will beunderstood, of course, that the actual speed signal generator 100 couldbe a hydraulic, mechanical or electrical device. The signal E, of theactual speed signal generator is fed to a preidle speed signal generator102 shown in FIG. 1. The preidle speed signal generator 102 delivers apressure signal to signal conduit when E, is at a value which isindicative of a predetermined speed slightly below that of ground idle.When land, 96 is exposed to this pressure signal via port 88, the spool92 is moved to the left, thereby placing inlet port 82 and outlet port84in fluid communication. Flow emerging from outlet port 84 of inletfuel shutoff valve 78 is directed to a high-low selector valve 104, thisvalve serving to direct fuel to either of the centrifugal pumps. Thehigh-low selector valve includes chambers 106 and 108 which areseparated by an annular abutment 110. Chamber 106 communicates withinlet port 112 and a highflow outlet port 114 and a low-flow outlet port116, these outlet ports being respectively connected to the highandlowflow centrifugal pumps. Chamber 108 of the high-low selector valve104 is in communication with signal ports 118 and 120. The dischargepressure in the main outlet conduit 68 is ducted by suitable means toport 118 of the high-low selector valve, and another signal pressurefrom the fuel control is ducted t0 the port 120. The signal communicatedto port 120 is indicative of the flow demanded of the control, as ismore fully explained hereinafter.

Spool 122 is slidingly disposed in the hole defined by the annularabutment 110 for sliding movement therein. Spool 122 comprises a land123 at the right end thereof which functions as a half area piston andis exposed to the pressure P and the signal pressure from the fuelcontrol. At the other end of spool 122 is secured a disc 124 having anintegral axial projection 126, the function of which is describedhereinafter. The walls of chamber 106 are provided with annular valveseats 128 and 130, on which the disc 124 is seatable. When the disc 124is seated upon seat 130, the flow is directed from inlet port 112 tooutlet port 114, which in turn communicates with the highflow pump.Conversely, when the disc 124 is seated upon seat 128, fuel is directedto the low-flow pump from inlet 112 to outlet 116.

The manner of operation of valve 104 is more fully described hereafter.For the purpose of describing the operation of the various flow circuitsin the unitized pump of the invention, it is sufficient to state thatwhen low-flow demands are placed on the fuel control, spool 112 occupiesa position to the left of that illustrated; whereas, when high-flowdemands are imposed upon the fuel control, the valve occupies theillustrated position.

Conduit 132 provides communication between high-flow outlet port 114 andthe inlet of a centrifugal inducer impeller pump 134. The discharge frompump 134 is directedvia a conduit 136 to the inlet of centrifugalimpeller pump 138. The discharge from impeller pump 138 is directed tothe fuel discharge manifold via conduit 140 and a spring-loaded checkvalve 142 which is mounted in chamber 72. The spring loading on checkvalve 142 urges it into a position in which it closes off the dischargemanifold from conduit 140. it will be noted that check valve 66 performsa similar function. It will also be noted that the back sides of thecheck valves 66 and 142 are exposed to discharge pressure in themanifold, the discharge pressure assisting and urging the check valvesto their closed positions.

The inducer impeller 134 of pump 138 is drivingly connected by a shaft144 to a gear 146 which functions as the input drive to inducer pump134. Gear 146 meshes with gear 46 of the positive displacement pump 42and has a larger diameter than gear 46 which, as noted heretofore, islarger than gear 44. Tl-lus, the gears 44 and 46 not only serve as agear pump, but also serve as a part of a gear drive train in associationwith gear 146, the gear 46 acting as an idler gear in the gear train.Shaft 148 drives impeller pump 138 by virtue of its being an extensionof shaft 52. Thus, rotation of shaft 52 simultaneously drives thepositive displacement pump 42 and impeller pump 138.

A second flow circuit is that defined by outlet 84, inlet 112, chamber106, outlet 114, conduit 132, inducer pump 134, conduit 136, impellerpump 138 and conduit 140. The second flow circuit is inactive uponengine startup in the sense that it is not delivering fuel during thisperiod to the discharge manifold. This inactivity of the second circuitis due to the c1osure of the inlet port 32 of the inlet fuel shutoffvalve 7%. The second circuit remains inactive until spool 92 is shiftedto the left by a pressure signal from conduit 90 and, as previouslymentioned, this signal is delivered when the engine reaches a speedslightly below that of ground idle.

It will be noted that while the second circuit will normally be activeafter the inlet port 32 of the inlet fuel shutoff valve 78 is initiallyopened, this will not be the case if the high-low selector valve spool122 is positioned to the left of the illustrated position in response tothe fuel control signal which reflects a low-flow demand upon the fuelcontrol system. In this position, the second circuit is blocked due tothe seating of disc 126 on seat 128. In this case, the third pumpingcircuit is activated. As noted above, the selection of the second orthird pumping circuit is dependent on the total fuel flow demanded ofthe fuel control, that is, the sum of the fuel flow to the augmentor Wand the fuel flow to the gas generator W Signals, reflecting the fuelflow demanded by the gas generator and the augmentor, are fed to asumming device 150 which produces a resultant signal reflecting thetotal demanded fuel flow (i.e., the total fuel flow to the engine). Thelatter signal is directed to a pump selector signal generator 152 whichis adapted to deliver a high-pressure signal to the high-low pumpselector valve when the demanded fuel flow is below a predeterminedlevel. The pump selector signal generator 152 has sufficient hysteresisso that operation is stable and frequent switching is avoided.

Assuming that the pump selector signal generator has requested operationon the low-flow pump, the high-low selector valve is positioned to portinlet fuel to the low-flow pump.

In this position, disc 124 is seated against seat 128. This, of

course, results from the high pressure communicated to the back ofpiston 123 via port 120. Thus, when the third pumping circuit isactivated due to a leftward displacement of spool 122, flow proceedsfrom the inlet fuel shutoff valve port 84 to inlet port ll 12 of thehigh-low selector valve 104 and thence to outlet port 1116.

A conduit 15d connects outlet port lll6 with a vapor core pump 158 whichincludes an axial inducer 1160 and an impeller 162. Impeller T62 ismounted on an extension of shaft 148 and is thus driven by input shaft52. The vapor core pump also includes a peripheral slotted window-typevapor core valve 164!- surrounding the eye of the axial inducer. Theposition of the vapor core valve 164 is controlled by movement of a link165, which in turn is controlled by a low-flow pump controller i168,which is discussed hereinafter. The construction and operation of vaporcore pumps and valves are described in great detail in the following US.Pat. Nos. 3,265,000; 3,142,255; 3,128,822; and 3,106,165. issued to S.R. Tyler. Reference is hereby made to these patents for a more detaileddiscussion of vapor core pumps and valves.

It will be noted that the actual speed signal generator 1100 senses thespeed of both centrifugal pumps, as this speed is proportional to thespeed of the engines due to their driving connection to the gear boxthereof. if desired, the actual speed signal generator could beconnected directly to shaft 52 and 1% since its primary function, withrespect to the instant invention, is to sense the speed of thecentrifugal pumps. This arrangement insures that an input flow will notbe directed to either of the centrifugal pumps until they reachrespective predetermined speeds.

The discharge from impeller 162 is delivered, via a conduit 170, to acheclt valve 172 which is similar in construction to the check valves 66and M2. Flow then proceeds into the discharge manifold from the outletof conduit 1170 via check valve 172.

In order to insure that either the second or third pumping circuit isvented when it is deactivated by displacement of the high-low selectorvalve, a vent valve, generally designated at 174, is provided to ventthe nonselected circuit. Vent valve ll'ld includes a chamber havinginlet ports 176 and 1170, and an outlet port 1100. The inlet ports 1176and 1178, are in respective fluid communication with conduits M0 and ofthe second and third pumping circuits respectively. A spool H02, havinglands 1% and 1186, is mounted within the chamber of vent valve 1174 foraxial sliding movement: therein. Connected to the left side of land 1176is a flanged structure m0 which is urged towards the right by acompression spring 100. The flanged structure 100 limits the rightwardtravel of spool 1102, as it is adapted to contact the housing "thereof.Spool 1102 is an axial alignment with projection H26 of the high-lowselector valve 1041. When the high-low selector valve is moved to theleft of the position illustrated, projection 1126 contacts land 1186 anddisplaces spool 1102 to the left against the urging of spring 1.90. itwill be observed that in the position shown, inlet port 1170 is incommunication with outlet port 100, thereby venting the third pumpingcircuit. However, when the second pumping circuit is deactivated, byvirtue of the seating of disc 124 of the high-low selector valve againstseat 120, projection l26 positions the spool so as to discontinue thefluid communication between ports 1170 and establish fluid communicationbetween ports 176 and 100. Thus, the pump positioned in the deactivatedcircuit is vented. Outlet port 180 of the vent valve 1174 is connectedto a conduit 100 which communicates with chamber 50.

A bypass pressure regulator valve 192 maintains a constant differentialpressure across the fuel control (e.g., 100 p.s.i.). Regulator valve l92comprises a housing having an elongated cavity therein. Cavity 1% has aninlet port 196 and an outlet port 198. The cavity 11% is also formedwith an annular portion 200. Pressure-sensing ports 202 and 204! aredisposed at the respective ends of the cavity 104 to transmit thepressure across the control to a spool 206, slideably mounted within thecavity. Spool 206 comprises a lower land 200 and an upper land 2110, theoutboard face of land 200 being exposed to the fuel controls dischargepressure P,, and the outboard face of land 2l0 being exposed to thecontrols inlet pressure and the outboard face of land 210 being exposedto the controls inlet pressure P,. A compression spring 212 is disposedin the lower part of the cavity 194 in contact with spool 208. Conduits21l4l and 216 respectively communicate with the pressures I? and l, totransmit these pressures to the pressure-sensing ports 202 and 204.

When the spool 206 is in its upper limit of travel, inlet port 196 isblocked by land 208, thereby preventing a bypass flow through the valveto conduit 36. When the spool 206 is disposed in positions lower thanthat of its upper limit of travel, at least partial communication isestablished between inlet port 1196 and outlet port 198, and hence somefuel is bypassed during operation of the positive displacement pump. Aspreviously mentioned, the regulator valve is designed to maintain apredetermined pressure drop across the fuel control. Therefore, assumingthat the positive displacement pump is in operation -that is, the firstpumping circuit -and that the valve is in the illustrated position, anincrease in the pressure differential (P -P produces a downward movementof spool 206, thereby increasing the amount of bypass flow. Should thepressure differential decrease, spool 206 will move upwardly, therebydecreasing the amount of bypass flow.

A conduit 220 is fluidly connected to conduit 62 at a loca tionintermediate the discharge of the positive displacement pump and checkvalve 66, conduit 220 being connected to inlet port 196 of the regulatorvalve. Therefore, during operation of the positive displacement pump,bypass flow is adapted to proceed from conduit 62 to outlet port 1190via conduit 220 and inlet port l96. The bypassed flow emerging fromoutlet port 190 joins with the input flow from the jet pump 24$ andflows via conduit 36 to the gear pump unloading valve 40 and thence tothe inlet of the positive displacement pump via conduit 30. Thedifferential pressure (P -P maintained by the regulator valve 192, isnot sufficient to actuate the gear pump unloading valve 40, andtherefore, this valve does not interfere with the bypass flow proceedingtherethrough to the inlet side of the positive displacement pump 42. Abypass circuit is then formed by conduit 220, regulator valve 192,conduit 36, unloading valve 40 and conduit 38.

Gear pump unloading valve 40 comprises a spool 222, which includes lands224. and 226, mounted in cylindrical cavity 228. Pressure-sensing ports230 and 232 communicate with the cavity 228 to respectively direct thepressures P and P, to the outboard faces of lands 226 and 224. Valve 40further includes outlet ports 234 and 236 and inlet port 238, as well asa discharge pressure transmittal port 240 disposed in the lower portionthereof.

Outlet port 234 is adapted to communicate with port 230, which is placedin communication with the fuel control inlet pressure P when spool 222is downwardly displaced. In order to produce such a displacement, it isnecessary to create a predetermined pressure differential (P, --P:)which is significantly greater than the differential maintained by theregulator valve 192. Outlet port 236 is in communication with inlet port238 during operation of the first pumping circuit, as the differentialpressure maintained by the regulator valve is not sufficient todownwardly displace spool 222. The discharge pressure transmittal port240 is in constant communication with the fuel control dischargepressure P irrespective of the position of the gear pump unloadingvalve, this port serving to transmit fuel control discharge pressure tothe outboard face of land 208 of the regulator valve via conduit 214.

When a signal from the preidle speed signal generator 102 actuates theinlet fuel shutoff valve 78 such that a flow commences in either thesecond or third pumping circuits, the

pressure difi'erential (Pr-P rises rapidly from the differentialpressure maintained by regulator valve 192 to a differential pressurewhich may be of the order of 150 p.s.i. This pressure differential issufficient to downwardly displace spool 222, thereby uncovering port 234and covering port 238. This results in a flow from port 230 to thenozzle 28 of the jet pump 24 via port 234 and conduit 242. Thisdifferential pressure occasioned by the operation of the second or thirdpumping circuits is also sufficient to downwardly displace spool 206, ofthe regulator valve 192, to its lower limit of travel, therebyestablishing untrammelled communication between port 196 and port 198.With the port 238 blocked by land 226, input flow cannot reach the inletof the positive displacement pump.

It will be recalled that the piston 54, which actuates the wear block 48of the positive displacement pump 42, urges the wear block against theteeth of gears 44 and 46 in response to the force exerted thereon byspring 60 and the pressure ported behind the right face of the piston 54via passage 58. A conduit 242, which interconnects the port 234 of thegear pump unloading valve and the nozzle 28 of the jet pump 24,comprises a branch conduit 244 which communicates with the left portionof cylinder 56. This connection enables the pressure in conduit 242 tobe ported to the left face of the piston 54 to move the wear block 48away from the gear teeth and thereby unload gear pump. Thus, thedownward displacement of the spool 222 of the gear pump unloading valvenot only cuts off fuel flow to the positive displacement pump, but alsocauses the wear block to move away from the gear teeth by virtue of thepressure ported from conduit 242.

During operation of the second or third pumping circuits, the jet pump24 is in operation. Fuel flowing from inlet port 230 of the gear pumpunloading valve is communicated to the nozzle 28 via port 234 andconduit 242. Nozzle 28 of the jet pump 24 discharges into venturisection 32, thereby creating a low pressure at the inlet 34 of the jetpump which induces a flow in the bypass conduit 220 to drain theformerly flooded gear cavity 50. Therefore, during operation of eitherthe second or third pumping circuits, fuel is withdrawn from cavity 50,via conduit 220, port 196, port 198 and conduit 36, to the inlet 34 ofthe jet pump. Flow then proceeds from the outlet of the jet jump toconduit 22 and rejoins the input flow in conduit 20. It will be notedthat the jet pump is in constant operation during fuel flow in eitherthe second or third pumping circuit.

As noted above, vent valve 174 assures that the deactivated centrifugalpumping circuit is vented during operation of the other centrifugalpumping circuit. When the second pumping circuit is in operatiomthehigh-low selector valve 104 and the vent valve 174 are in theillustrated positions, and therefore the low-flow vapor core pump 158 isvented to the chamber 50 of the positive displacement pump via conduit170, ports 178 and 180 and conduit 190. As the jet pump 24 is incontinuous operation during operation of either the second or thirdpumping circuit, the chamber 50 is continuously vented.

When the third pumping circuit is activated, due to the shifting ofspool 122 to the left, projection 126 contacts land 186 of spool 182 tothereby shift spool 182 to the left. Leftward motion of the spool 182results in the uncovering of port 176 of vent valve 174, therebyestablishing communication between ports 176 and 180. Centrifugal pump138 is thereby vented via port 176,180 and conduit 190.

it will be noted that with respect to the low-flow vapor core pump andthe high-flow pump, this venting is mutually exclusive. The venting ofthe second and third pumping circuits through chamber 50 tends toeliminate windmilling losses which might otherwise be encountered in theinactive pumping circuit.

By way of general comment, the principal flow paths through the first,second and third pumping circuits are indicated in FIG. 2 by the solidarrows, dashed headed arrows and phantom arrows respectively.Furthermore, it will be understood that the check valves in each of thepumping circuits are closed when the particular pumping circuit isinactive, and opened when the particular pumping circuit is active. Whena switch is made from the first flow circuit to the second flow circuit,the pressure rises rapidly in conduit 140 to a value which is sufficientto open check valve 142. The subsequently increased pressure in thedischarge manifold effects a closing of check valve 66. When a switch ismade from the second flow circuit to the third flow circuit, or viceversa, the pressure upstream of the previously opened check valve dropsso that the previously opened check valve moves to a closed position.include Referring again to FIGS. 1A and 18, it can be seen that conduit68 bifurcates to direct the fuel flow from the pump into parallel fuelmetering lines 250 and 252, the lines 250 and 252 respectively supplyingfuel to the gas generator and the augmentor. Line 250 includes a gasgenerator fuel-metering valve 254 which meters the fuel flowingtherethrough. Line 252 also includes a metering valve 256 which metersfuel flow to the augmentor. Lines 250 and 252 include respectivedifferential pressure regulators 258 and 260. These in-line regulatorsare preferably of the proportional plus integral type which permit fastresponse in the proportional mode to minimize the total quantity of fuelmetered in error during the transient. The differential pressureregulators are adapted to maintain a constant pressure differentialacross the respective fuel-metering valves so that the fuel flow in eachof the lines is purely a function of the area of the metering orifice ofthe valve associated with the line. At the ends of the lines 250 and252, shutoff valves 262 and 264 are provided to respectively shut offfuel flow to the gas generator and augmentor.

The metering system per se is conventional and has been usedsuccessfully in numerous jet engine fuel systems. Because of thepressure-flow characteristic of a centrifugal pump (variation in fuelflow rate has only a minor influence on discharge pressure), theoperation of the two metering systems in parallel off of a noninletthrottled centrifugal pump causes no dynamic difficulty.

Pressure-sensing lines 266 and 268 respectively communicate with thelines 250 and 252 intermediate the metering and shutoff valves thereof.These pressures, which are respectively denoted P and P are directed toa select highest valve 270 which directs the largest of the pressures P,and P to the low-flow pump controller 168, regulator valve 192, and gearpump unloading valve 40, the highest pressure being denoted P 9-OPERATION Start and Acceleration to Idle Referring to FIGS. llA, BB and2, with particular emphasis on FIGS. IA and EB, it will be observed thatstarting and acceleration to idle are fully automatic. As the gasgenerator spool speed increases, the input flow in conduit 20 entersconduit 22 and proceeds therefrom to the inlet of positive displacementpump 42 via jet pump 24, conduit 36, gear pump unloading valve 40 andconduit 39. During this phase of operation, inlet port 82, of the inletfuel shutoff valve 78, is blocked by land 94, thereby preventing fuelflow to either of the centrifugal pumps. Fuel then passes from theoutlet of the positive displacement pump 42 through conduit 62 into thedischarge manifold. When the discharge pressure is sufficient toovercome the spring preload on check valve 66, fuel from the dischargemanifold proceeds to the fuel control via conduit 68. As the dischargepressure at the outlet of the positive displacement pump increases, thesealing force exerted on the gears 44 and 46 correspondingly increasesdue to the discharge pressure being ported behind the piston 54 viapassage 58. Fuel flows from conduit 68 into fuel line 250 as thereusually will be no initial fuel flow in conduit 252, since augmentoroperation is normally not required below l/percent engine speed.Therefore, shutoff valve 264 will be closed until this speed isattained. Fuel thence passes through differential pressure regulator 253and gas generator fuel metering valve 254, the differential pressurethereacross being maintained essentially constant by regulator 2%. Flowemerges from the metering valve 254 and proceeds to the engine viashutoff valve 262.

The pressure at the inlet to the fuel control P and the pressure P inthe line 250, intermediate fuel-metering valve 264 and shutoff valve262, are transmitted to the regulator valve 192 and the gear pumpunloading valve 40, the pressure P, being directed thereto via selecthighest valve 270. When the differential pressure across the fuelcontrol (PfPg) attains a predetermined value (e.g., I00 p.s.i.),regulator valve 192 commences to function to maintain this differentialpressure. Fuel is now bypassed via conduit 62, conduit 220, regulatorvalve 192, conduit 36 gear pump unloading valve 40 and conduit 38. Asnoted above, the gear pump unloading valve is in the illustratedposition during this mode of operation, and therefore the bypass flow isnot impeded thereby.

When the engine of FIG. 3 reaches a speed slightly below that of groundidle, the signal E,,, from the actual speed signal generator, actuatesthe preidle speed signal generator 102, which results in a pressuresignal being directed to inlet fuel shutoff valve 78 via conduit 90.Under the influence of the high pressure in chamber 80 occasioned bythis pressure signal, the spool 92 is shifted to the left of theillustrated position of FIG. 2 thereby establishing fluid communicationbetween ports 62 and 84 of inlet fuel shutoff valve '78. The shifting ofvalve 92 may be considered the prelude to the deactivation of the firstpumping circuit and the activation of either the second or third pumpingcircuit.

Operation on the High Flow Pump If the engine is started at a lowaltitude, in all probability operation on the high-flow pump will beinitiated when the engine reaches a speed slightly below that of groundidle. In the event that the engine is started at a high altitude,operation on the low-flow pump will likely follow the deactivation ofthe first pumping circuit. It will be noted that the controlling factorin the selection of either the second pumping circuit or third pumpingcircuit is the fuel flow demanded by the engine.

Therefore, assuming the sum of the fuel flow requested of the gasgenerator circuit W and the fuel flow requested of the augmentor circuitW is a requested total fuel flow W which is not of a magnitude to directthe pump selector signal generator to deliver a high-pressure signal toport 1120 of the high-low selector valve, the spool 222 thereof will bein the il lustrated position in FIG. 2 when spool 92 of the inlet fuelshutoff valve Ill shifts to the left. 'In this mode of operation, fuelfrom inlet conduit simultaneously flows through both the llllll firstpumping circuit and the second pumping circuit. Flow then proceeds inthe second pumping circuit from inlet port 82 to outlet port 84, fromwhere it enters the inlet port 112 of the high-low selector valve 104.Fuel from the high-low selec' tor valve emerges at outlet port 114 andpasses through conduit I132 to inducer 34, from where it is delivered tothe highflow centrifugal pump R36 via conduit 1136. Flow emerging fromthe centrifugal pump I38 proceeds to the discharge manifold via conduit140 when the pressure therein is suffcient to overcome the spring andpressure load of check valve 142.

As the differential pressure (P -P increases due to the flow in thesecond pumping circuit, the respective spools of the regulator valve andthe gear pumping unloading valve are displaced in a downward manner,thereby providing an unobstructed bypass flow path through the regulatorvalve and blocking the flow of inlet fuel to the inlet of the positivedisplacement pump 42. Displacement of spool 222 of the gear pumpunloading valve produces a communication between port 230 and port 234which results in a flow through conduit 242 to the nozzle 28 of the jetpump 24. The pressure in conduit 242 (I5) is communicated to theleft-hand portion of chamber 56 of the positive displacement pump,thereby displacing the piston, and hence the wear block 43, to theright. The rightward displacement of the wear block 48 serves to reducethe pressure at the outlet of positive displacement pump 42. Therefore,the sequential action of the gear pump unloading valve and the wearblock 48 occasions an unloading of the positive displacement pump 42.

The jet pump is now in operation since the unloading of the positivedisplacement pump 42 initiates operation of the jet pump 24, and thusthe cavity 50 is vented via the outlet of the positive displacement pumpconduit 62, conduit 220, port 1196, port 193 and conduit 36. The suctioncreated by the flow through nozzle 28 of the jet pump 24 provides thepressure differential for the flow in this flow path. The low-flow vaporcore pump 158 is vented during operation of the second pumping circuitvia conduit 170, ports 1178 and 1180 and conduit 190, the vent flowproceeding into cavity 50, from where it proceeds to the jet pump viaabove-described route. Flow from the jet pump enters conduit 22 and isthence delivered to inlet conduit 20 where it rejoins the input flow. Itwill be that during the switching operation from the first pumpingcircuit to the second pumping circuit, the flow in conduits 22 and 36 isreversed.

Operation in the high-flow pump mode (second pumping circuit) is thebasic system and does not require a pump control loop. The high-flowpump provides an essentially constant pressure source of fuel to boththe gas generator and augmentor fuel-metering system. As shown in FIG.4, high-flow pump pressure is always at least p.s.i. above the engineback pressure.

During operation of the second pumping circuit, the augmentor may beutilized to provide additional thrust by opening shutoff valve 264. Inthis case, flow discharged from the discharge manifold of the unitizedpump enters conduits 250 and 252 and passes through the respectivepressure regulators, metering valves and shutoff valves. The parallelflows of fuel emerging from the shutoff valves 262 and 264 arerespectively directed to the gas generator and the augmentor.

Switching to operation on either the low-flow pump'with inlet throttlingor the positive displacement pump is accomplished such that therespective fuel-metering systems, for the gas generator and theaugmentor, operate in a continuous fashion. At most, only an inletpressure disturbance will be encountered during switching.

Operation on the Low-Flow Pump The total amount of gas generator plusaugmentor fuel metered to the engine is computed in the fuel control bysummer 150. Should the total fuel signal from the summer to the pumpselector signal generator correspond to a predetermined lowflow, pumpselector signal generator 1152 will, upon receipt of the signal, directa high-pressure signal to the high-low selector valve 104 via port 120thereof. The pressure communicated to the right face of piston 123 bythe pump selector signal generator is sufficient to displace spool 122in a leftward direction into seating engagement with seat 128.

As noted heretofore, during leftward movement of spool 122, projection126 displaces spool 182 of vent valve 174 to the left, thereby coveringport 178 and uncovering port 176. This movement of spool 182 results ina discontinuation of the venting of low-flow pump 158 and an initiationof the venting of high-flow pump 138, the high-flow. pump being ventedvia conduit 140, port 176, port 180 and conduit 190. After the disc 124of the high-low selector valve is seated on seat 128, flow through thesecond pumping circuit is curtailed and flow communication isestablished between ports 112 and 116, thereby allowing flow to proceedto the inlet of the low-flow vapor core pump 158, this flow proceedingvia conduit 154. The discharge from the low-flow pump 158 is directed tothe discharge manifold via conduit 170 when the pressure therein issufficient to overcome the spring preload of check valve 172. Asmentioned above, the pump selector signal generator 152 has sufficienthysteresis so that operation is stable and frequent switching isavoided.

The low-flow pump controller 168 senses the pressures P and accordinglypositions inlet throttling valve 164 of lowflow pump 158. OPeration onthe low-flow pump is similar to operation on the positive displacementpump to the extent that the gross pressure differential (P -P across thefuel-metering system is regulated. During operation of the third pumpingcircuit, this differential pressure is maintained at a higher value thanthat which was maintained during operation of the positive displacementpump. For purposes of illustration, assume that the differentialpressure maintained across the fuel control by the low-flow pumpcontroller is 150 psi. Thus, the low-flow pump controller 168continuously positions the inlet throttling valve 164 of the low-flowpump 158 during operation of the third pumping circuit to maintain apredetermined pressure differential across the fuel control.

It should be noted that when operating in the augmentation mode duringoperation of the third pumping circuit, the control system automaticallyselects the higher of the two metered pressures P, and P downstream ofthe gas generator and augmentor metering valves, and that duringoperation of the third pumping circuit, the low-flow pump controller 168regulates fuel control inlet pressure P to be a predetermined amountl50p.s.i.) above the highest of the two metered pressures. Therefore,the metering system operating at the lower metering valve dischargepressure operates with a greater pressure drop across its metering headregulaton' Pump-Control System Perfonnance Turning now to FIG. 4 apressure versus total fuel flow chart shows the characteristics of atypical pump-control system constructed in accordance with the teachingsherein. As the curve representing the discharge pressure envelope of thefuel control show, the discharge pressure P decreases as the fuel flowrequired by the engine decreases, the shape of this curve beingdetermined by the particular back pressure characteristics of the enginesought to be controlled. When the requested fuel flow reaches s apredetermined value, the third pumping circuit is activated, aspreviously described, and therefore there fuel control inlet pressure Pdecreases with the decreasing fuel flow requirements such that P, ismaintained equal to P plus a constant differential pressure (150p.s.i.). Maintenance of this differential pressure is, of course, due tomodulation of the inlet valve by the low-flow pump controller. Thelow-flow pump inlet pressure curve portrays the relationship between therequested fuel flow and inlet pressure when the inlet throttling valve164 provides a maximum inlet area. The pressure decreases due to inletthrottling for a given fuel flow is easily ascertained at any operatingpoint. For a sample case, FIG. 4 shows, on the low-flow pump pressureversus flow curve, the operating point after the inlet has been throttleto an area A the point being circled. The pump inlet throttling valvereduces the pressure rise across the pump, thereby reducing the pumpinput horsepower and minimizing fuel temperature rise.

It is to be understood that the particular embodiment of the inventionas described above and shown in the accompanying drawings, is merelyillustrative of and not restrictive on the broad invention, and thatvarious changes in design structure and arrangement may be made withoutdeparting from the spirit and scope of the appended claims.

I claim:

1. In a device for controlling the flow of a fluid a fluid-consumingload, the combination comprising:

a unitized pump having two pumping circuits for delivering fluid to theload;

a low-flow centrifugal pump positioned in the other of the circuits topump the fluid therethrough; high-flow centrifugal pump positioned inone of the circuits to pump the fluid therethrough;

a positionable selector operatively connected to both of the circuitsfor directing an input flow of the fluid to either the one or the othercircuit;

a pump selector signal generator operatively connected to the selectorto generate a signal thereto for the positioning thereof; and

means responsive to the total fluid flow delivered to the load tocontrol the signal generator.

2. The combination, as defined in claim 1 wherein the unitized pumpfurther comprises:

an additional pumping circuit;

a positive displacement pump positioned in the additional pumpingcircuit to pump the fluid therethrough; and

a shutoff off valve disposed in fluid communication with the inlet ofthe pump and operatively connected to the first mentioned two pumpingcircuits for preventing an input flow thereto until at least one of thecentrifugal pumps attains a predetermined speed, the shutofl" valvebeing remotely located from the additional pumping circuit so as not toimpede an input flow thereto.

3. The combination, as defined in claim 2, further including:

means responsive to the speed of at least one of the centrifugal pumpsto generate a speed signal to the shutofi valve for opening the shutoffvalve.

4. In a device for controlling the flow of a fluid-consuming load, thecombination comprising:

a unitized pump having an inlet conduit, an outlet conduit, a firstpumping circuit and a second pumping circuit, the pumping circuits eachbeing in fluid communication with the inlet and outlet conduits andbeing adapted to deliver the fluid to the load;

a positive displacement pump positioned in the first pumping circuit topump the fluid therethrough;

a centrifugal pump positioned in the second pumping circuit to pump thefluid therethrough;

a metering system fluidly connected to the outlet conduit of theutilized pump for metering a flow of fluid to the load;

a shutoff valve fluidly connected to the inlet conduit and the secondcircuit for preventing a flow of the fluid from the inlet conduit to thesecond circuit; and

means to sense the speed of the centrifugal pump and generate a signalto open the shutoff valve when the centrifugal pump attains apredetermined speed.

5. The combination, as defined in claim 4, wherein the unitized pumpincludes:

means to maintain a constant pressure differential across the meteringsystem during operation of the positive displacement pump.

6. The combination, as defined in claim 4, wherein the unitized pumpincludes:

a third pumping circuit;

a low-flow centrifugal pump positioned in the third pumping circuit topump the fluid therethrough from the inlet conduit to the outletconduit; and

a positionable selector operatively connected to both the second andthird pumping circuits for directing an input flow in the inlet conduitto either the second or third pumping circuit.

7. The combination, as defined in claim 6, further including:

means responsive to the flow in the metering system to control theposition of the selector.

8. The combination, as defined in claim 6, wherein the unitized pumpincludes:

means to maintain a constant pressure differential across the meteringsystem when the low-flow pump is in operation.

9. In an afterburning-type pump-control system for delivering fuel to anengine, the combination comprising:

a unitized pump having an inlet, an outlet and two pumping circuitsadapted to respectively communicate with both the inlet and the outlet;

a high-flow centrifugal pump positioned in one of the circuits to pumpthe fuel therethrough;

a low-flow centrifugal pump positioned in the other of the circuits topump the fuel therethrough;

a positionable selector operatively connected to both of the circuitsfor directing an input fuel flow from the inlet to either the one or theother circuits;

two fuel lines fluidly connected to the outlet for receiving a flow offuel therefrom;

two metering devices respectively connected to the lines for meteringfuel flows therethrough;

a pump selector signal generator operatively connected to the selectorto generate a signal thereto for the positioning thereof; and

means responsive to the total fuel flow in the lines to control thesignal generator.

it). The combination, as defined in claim 9, wherein the unitized pumpfurther comprises:

an additional pumping circuit adapted to communicate with the inlet andthe outlet;

a positive displacement pump positioned in the additional pumpingcircuit to pump the fuel therethrough; and

a shutoff valve disposed in fluid communication with the inlet of theunitized pump and operatively connected to the first mentioned twopumping circuits for preventing an input fuel flow thereto until theengine attains a predetermined speed, the shutoff valve being remotelylocated from the additional pumping circuit so as not to impede an inputflow thereto.

ill. The combination, as defined in claim it), further includmeansresponsive to the speed of the engine to generate a speed signal to theshutoff valve for opening the shutoff valve.

12. In an afterburning-type pump-control system for delivering fuel toan engine, the combination comprising:

a unitized pump having an inlet, an outlet, a first pumping circuit anda second pumping circuit, the pumping circuits each being in fluidcommunication with the inlet and the outlet, and each being adapted todeliver the fuel to the engine; h

a positive displacement pump positioned in the first pumping circuit topump the fuel therethrough;

a centrifugal pump positioned in the second pumping circuit to pump thefuel therethrough;

two fuel lines fluidly connected to the outlet for receiving a flow offuel therefrom;

two metering devices respectively connected to the lines for meteringfuel flows therethrough;

a shutoff valve fluidly connected to the inlet and the second circuitfor preventing a flow of fuel from the inlet to the second circuit, theshutoff valve being remotely located from the first circuit so as not toimpede an input flow thereto; and

means to sense the speed of the centrifugal pump and generate a signalto open the shutoff valve when the centrifugal pump attains apredetermined speed.

13. The combination, as defined in claim 112, wherein the unitized pumpfurther includes:

lid

higher of the respective pressures downstream of the metering devicesduring operation of the positive displacement pump.

M. The combination, as defined in claim 112, wherein the unitized pumpfurther includes:

a third pumping circuit adapted to fluidly communicate with the inletand the outlet;

a low-flow centrifugal pump positioned in the third pumping circuit topump fuel therethrough from the inlet to the outlet; and

a positionable selector operatively connected to the second and thirdpumping circuits for directing an input flow from the inlet to eitherthe second or third pumping circuits.

l5. The combination, as defined in claim M, further includ ing:

means responsive to the total flow in the fuel lines to control theposition of the selector.

116. The combination, as defined in claim M, further including:

means to maintain a constant pressure differential between the pressureat the outlet of the unitized pump and the higher of the respectivepressures downstream of the metering devices during operation of thelow-flow pump.

17. A unitized pump for pumping a fluid comprising:

an inlet conduit;

an outlet conduit;

a first pumping circuit adapted to communicate with the inlet and outletconduits;

a positive displacement pump having an inlet and an outlet positioned inthe first pumping circuit to pump the fluid therethrough;

a second pumping circuit adapted to communicate with the inlet andoutlet conduits;

a centrifugal pump positioned in the second pumping circuit to pump thefluid therethrough;

a bypass circuit in fluid communication with the outlet and inlet of thepositive displacement pump to bypass an outlet flow back to inlet;

a regulator valve mounted in the bypass circuit to control the flowtherein; and

an unloading valve positioned in the bypass circuit inter mediate theregulator valve and the inlet of the positive displacement pump, theunloading valve being positionable to prevent a flow to the inlet of thepositive displacement pump.

llfl. A pump, as defined in claim l7, wherein the positive displacementpump comprises:

a housing having a pumping cavity therein, the cavity communicating withthe inlet and outlet of the positive displacement pump;

a pair of intermeshing gears disposed in the cavity; and

sealing means to move into peripheral engagement with the peripheries ofthe gears; and wherein there is further provided;

conduit means to interconnect the unloading valve and the sealing meansto move the sealing means out of peripheral engagement with the gears.

19. A pump, as defined in claim 18, further including:

a third pumping circuit adapted to communicate with the inlet and outletconduits; and

a low-flow centrifugal pump positioned in the third pumping circuit topump the fluid therethrough.

20. A pump, as defined in claim 19, further including:

a shutoff valve disposed in fluid communication with the inlet conduitand operatively connected to the second and third pumping circuits forpreventing an input flow thereto until at least one of the centrifugalpumps attains a predetermined speed, the shutoff valve being remotelylocated from the first pumping circuit so as not to impede an input flowthereto.

21. A pump, as defined in claim 19, further including:

drive means to drivingly interconnect the positive displacement pumpwith the centrifugal and low-flow centrifugal pumps.

22. A pump, as defined inclairn 19, further including:

a positionable selector operatively connected to both the second andthird pumping circuits for directing an input flow to either the secondor third pumping circuits.

23. A unitized pump for pumping a fluid comprising:

an inlet conduit;

an outlet conduit;

a first pumping circuit adapted to communicate with the inlet and outletconduits;

a positive displacement pump positioned in the first pumping circuit topump the fluid therethrough;

a second pumping circuit adapted to communicate with the inlet andoutlet conduits;

a high-flow centrifugal pump positioned in the second pumping circuit topump the fluid therethrough;

a third pumping circuit adapted to communicate with the inlet and outletconduits;

a low-flow centrifugal pump positioned in the third pumping circuit topump the fluid therethrough; and

a shutoff valve disposed in fluid communication with the inlet conduitand operatively connected to the second and third pumping circuits forpreventing a flow thereto until at least one of the centrifugal pumpsattains a predetermined speed, the shutoff valve being located remotefrom the first pumping circuit so as not to impede a flow thereto fromthe inlet conduit.

24. A unitized pump for pumping a fluid comprising:

an inlet conduit;

an outlet conduit;

a firstpumping circuit adapted to communicate with the inlet and outletconduits;

a positive displacement pump having an inlet and an outlet positioned inthe first pumping circuit to pump the fluid therethrough;

a second pumping circuit adapted to communicate with the inlet andoutlet conduits;

a high-flow centrifugal pump positioned in the second pumping circuit topump the fluid therethrough;

a third pumping circuit adapted to communicate with the inlet and outletconduits;

a low-pass centrifugal pump positioned in the third pumping circuit at alocation downstream of the inlet conduit to pump the fluid therethrough;

a bypass circuit in fluid communication with the outlet and inlet of thepositive displacement pump to bypass an outlet flow therefrom back tothe inlet thereof; and

a regulator valve mounted in the bypass circuit to control the flowtherein.

25. A pump, as defined in claim 24, further including:

drive means to drivingly interconnect the positive displacement pumpwith the high-flow and low-flow centrifugal pumps.

26. A pump, as defined in claim 24, further including:

a positionable selector operatively connected to the second and thirdpumping circuits for directing an input flow to either the second orthird pumping circuits.

my UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,614,269 Dated October 19, 1972 M H Robert S. Lanctot It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 49, change Patent No. "2,705,259" to 2,105,259

Column 3, line 53, change "93" to 92 Column 5, line 51, change PatentNo. "3,142,255" to 3,142,259

Column 8, line 39, delete include Column 12, line 10 (Claim 1, line 1),after "fluid" (first occurrence) insert to Column 12, line 14 (Claim 1,line 5) change "the other" to one Column 12, line 15 (Claim 1, line 6)change "high-flow" to low-flow Column 12, line 16 (Claim 1, line 7)change "one" to the other Column 12, line 42 (Claim 4, line 1) after"fluid" insert to a fluid Column 16, line 14 (Claim 24, line 15) change"low-pass" to low-flow Signed and sealed this 8th day of May 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. In a device for controlling the flow of a fluid a fluidconsumingload, the combination comprising: a unitized pump having two pumpingcircuits for delivering fluid to the load; a low-flow centrifugal pumppositioned in the other of the circuits to pump the fluid therethrough;high-flow centrifugal pump positioned in one of the circuits to pump thefluid therethrough; a positionable selector operatively connected toboth of the circuits for directing an input flow of the fluid to eitherthe one or the other circuit; a pump selector signal generatoroperatively connected to the selector to generate a signal thereto forthe positioning thereof; and means responsive to the total fluid flowdelivered to the load to control the signal generator.
 2. Thecombination, as defined in claim 1 wherein the unitized pump furthercomprises: an additional pumping circuit; a positive displacement pumppositioned in the additional pumping circuit to pump the fluidtherethrough; and a shutoff off valve disposed in fluid communicationwith the inlet of the pump and operatively connected to the firstmentioned two pumping circuits for preventing an input flow theretountil at least one of the centrifugal pumps attains a predeterminedspeed, the shutoff valve being remotely located from the additionalpumping circuit so as not to impede an input flow thereto.
 3. Thecombination, as defined in claim 2, further including: means responsiveto the speed of at least one of the centrifugal pumps to generate aspeed signal to the shutoff valve for opening the shutoff valve.
 4. In adevice for controlling the flow of a fluid-consuming load, thecombination comprising: a unitized pump having an inlet conduit, anoutlet conduit, a first pumping circuit and a second pumping circuit,the pumping circuits each being in fluid communication with the inletand outlet conduits and being adapted to deliver the fluid to the load;a positive displacement pump positioned in the first pumping circuit topump the fluid therethrough; a centrifugal pump positioned in the secondpumping circuit to pump the fluid therethrough; a metering systemfluidly connected to the outlet conduit of the utilized pump formetering a flow of fluid to the load; a shutoff valve fluidly connectedto the inlet conduit and the second circuit for preventing a flow of thefluid from the inlet conduit to the second circuit; and means to sensethe speed of the centrifugal pump and generate a signal to open theshutoff valve when the centrifugal pump attains a predetermined speed.5. The combination, as defined in claim 4, wherein the unitized pumpincludes: means to maintain a constant pressure differential across themetering system during operation of the positive displacement pump. 6.The combination, as defined in claim 4, wherein the unitized pumpincludes: a third pumping circuit; a low-flow centrifugal pumppositioned in the third pumping circuit to pump the fluid therethroughfrom the inlet conduit to the outlet conduit; and a positionableselector operatively connected to both the second and third pumpingcIrcuits for directing an input flow in the inlet conduit to either thesecond or third pumping circuit.
 7. The combination, as defined in claim6, further including: means responsive to the flow in the meteringsystem to control the position of the selector.
 8. The combination, asdefined in claim 6, wherein the unitized pump includes: means tomaintain a constant pressure differential across the metering systemwhen the low-flow pump is in operation.
 9. In an afterburning-typepump-control system for delivering fuel to an engine, the combinationcomprising: a unitized pump having an inlet, an outlet and two pumpingcircuits adapted to respectively communicate with both the inlet and theoutlet; a high-flow centrifugal pump positioned in one of the circuitsto pump the fuel therethrough; a low-flow centrifugal pump positioned inthe other of the circuits to pump the fuel therethrough; a positionableselector operatively connected to both of the circuits for directing aninput fuel flow from the inlet to either the one or the other circuits;two fuel lines fluidly connected to the outlet for receiving a flow offuel therefrom; two metering devices respectively connected to the linesfor metering fuel flows therethrough; a pump selector signal generatoroperatively connected to the selector to generate a signal thereto forthe positioning thereof; and means responsive to the total fuel flow inthe lines to control the signal generator.
 10. The combination, asdefined in claim 9, wherein the unitized pump further comprises: anadditional pumping circuit adapted to communicate with the inlet and theoutlet; a positive displacement pump positioned in the additionalpumping circuit to pump the fuel therethrough; and a shutoff valvedisposed in fluid communication with the inlet of the unitized pump andoperatively connected to the first mentioned two pumping circuits forpreventing an input fuel flow thereto until the engine attains apredetermined speed, the shutoff valve being remotely located from theadditional pumping circuit so as not to impede an input flow thereto.11. The combination, as defined in claim 10, further including: meansresponsive to the speed of the engine to generate a speed signal to theshutoff valve for opening the shutoff valve.
 12. In an afterburning-typepump-control system for delivering fuel to an engine, the combinationcomprising: a unitized pump having an inlet, an outlet, a first pumpingcircuit and a second pumping circuit, the pumping circuits each being influid communication with the inlet and the outlet, and each beingadapted to deliver the fuel to the engine; a positive displacement pumppositioned in the first pumping circuit to pump the fuel therethrough; acentrifugal pump positioned in the second pumping circuit to pump thefuel therethrough; two fuel lines fluidly connected to the outlet forreceiving a flow of fuel therefrom; two metering devices respectivelyconnected to the lines for metering fuel flows therethrough; a shutoffvalve fluidly connected to the inlet and the second circuit forpreventing a flow of fuel from the inlet to the second circuit, theshutoff valve being remotely located from the first circuit so as not toimpede an input flow thereto; and means to sense the speed of thecentrifugal pump and generate a signal to open the shutoff valve whenthe centrifugal pump attains a predetermined speed.
 13. The combination,as defined in claim 12, wherein the unitized pump further includes:means to maintain a constant pressure differential between the pressureat the outlet of the unitized pump and the higher of the respectivepressures downstream of the metering devices during operation of thepositive displacement pump.
 14. The combination, as defined in claim 12,wherein the unitized pump further includes: a third pumping circuitadapted to fluidly communicate with the inlet and the outleT; a low-flowcentrifugal pump positioned in the third pumping circuit to pump fueltherethrough from the inlet to the outlet; and a positionable selectoroperatively connected to the second and third pumping circuits fordirecting an input flow from the inlet to either the second or thirdpumping circuits.
 15. The combination, as defined in claim 14, furtherincluding: means responsive to the total flow in the fuel lines tocontrol the position of the selector.
 16. The combination, as defined inclaim 14, further including: means to maintain a constant pressuredifferential between the pressure at the outlet of the unitized pump andthe higher of the respective pressures downstream of the meteringdevices during operation of the low-flow pump.
 17. A unitized pump forpumping a fluid comprising: an inlet conduit; an outlet conduit; a firstpumping circuit adapted to communicate with the inlet and outletconduits; a positive displacement pump having an inlet and an outletpositioned in the first pumping circuit to pump the fluid therethrough;a second pumping circuit adapted to communicate with the inlet andoutlet conduits; a centrifugal pump positioned in the second pumpingcircuit to pump the fluid therethrough; a bypass circuit in fluidcommunication with the outlet and inlet of the positive displacementpump to bypass an outlet flow back to inlet; a regulator valve mountedin the bypass circuit to control the flow therein; and an unloadingvalve positioned in the bypass circuit intermediate the regulator valveand the inlet of the positive displacement pump, the unloading valvebeing positionable to prevent a flow to the inlet of the positivedisplacement pump.
 18. A pump, as defined in claim 17, wherein thepositive displacement pump comprises: a housing having a pumping cavitytherein, the cavity communicating with the inlet and outlet of thepositive displacement pump; a pair of intermeshing gears disposed in thecavity; and sealing means to move into peripheral engagement with theperipheries of the gears; and wherein there is further provided; conduitmeans to interconnect the unloading valve and the sealing means to movethe sealing means out of peripheral engagement with the gears.
 19. Apump, as defined in claim 18, further including: a third pumping circuitadapted to communicate with the inlet and outlet conduits; and alow-flow centrifugal pump positioned in the third pumping circuit topump the fluid therethrough.
 20. A pump, as defined in claim 19, furtherincluding: a shutoff valve disposed in fluid communication with theinlet conduit and operatively connected to the second and third pumpingcircuits for preventing an input flow thereto until at least one of thecentrifugal pumps attains a predetermined speed, the shutoff valve beingremotely located from the first pumping circuit so as not to impede aninput flow thereto.
 21. A pump, as defined in claim 19, furtherincluding: drive means to drivingly interconnect the positivedisplacement pump with the centrifugal and low-flow centrifugal pumps.22. A pump, as defined in claim 19, further including: a positionableselector operatively connected to both the second and third pumpingcircuits for directing an input flow to either the second or thirdpumping circuits.
 23. A unitized pump for pumping a fluid comprising: aninlet conduit; an outlet conduit; a first pumping circuit adapted tocommunicate with the inlet and outlet conduits; a positive displacementpump positioned in the first pumping circuit to pump the fluidtherethrough; a second pumping circuit adapted to communicate with theinlet and outlet conduits; a high-flow centrifugal pump positioned inthe second pumping circuit to pump the fluid therethrough; a thirdpumping circuit adapted to communicate with the inlet and outletconduits; a low-flow centrifugal pump positionEd in the third pumpingcircuit to pump the fluid therethrough; and a shutoff valve disposed influid communication with the inlet conduit and operatively connected tothe second and third pumping circuits for preventing a flow theretountil at least one of the centrifugal pumps attains a predeterminedspeed, the shutoff valve being located remote from the first pumpingcircuit so as not to impede a flow thereto from the inlet conduit.
 24. Aunitized pump for pumping a fluid comprising: an inlet conduit; anoutlet conduit; a first pumping circuit adapted to communicate with theinlet and outlet conduits; a positive displacement pump having an inletand an outlet positioned in the first pumping circuit to pump the fluidtherethrough; a second pumping circuit adapted to communicate with theinlet and outlet conduits; a high-flow centrifugal pump positioned inthe second pumping circuit to pump the fluid therethrough; a thirdpumping circuit adapted to communicate with the inlet and outletconduits; a low-pass centrifugal pump positioned in the third pumpingcircuit at a location downstream of the inlet conduit to pump the fluidtherethrough; a bypass circuit in fluid communication with the outletand inlet of the positive displacement pump to bypass an outlet flowtherefrom back to the inlet thereof; and a regulator valve mounted inthe bypass circuit to control the flow therein.
 25. A pump, as definedin claim 24, further including: drive means to drivingly interconnectthe positive displacement pump with the high-flow and low-flowcentrifugal pumps.
 26. A pump, as defined in claim 24, furtherincluding: a positionable selector operatively connected to the secondand third pumping circuits for directing an input flow to either thesecond or third pumping circuits.